Many of our modern devices make use of internal combustion engines. Typically associated with an internal combustion engine, will be a fuel reservoir such as a gas tank. In many applications, unwanted third party access to the gas tank is to be prevented. Therefore, especially in the automotive field, there have been developed what are generally referred to as lockable gas caps.
A lockable gas cap is a gas cap which includes a plug element, for plugging the filling tube of the gas tank, and, a handle element which may be gripped to remove the plug element from the mouth of the filling tube. Typically, a lock is mounted between the handle and the plug element for selectively locking the two components together. Thus, when the handle is locked to the plug element, the handle and the plug element may be rotated together, and therefore, the plug may be removed from the mouth of the filler tube. Similarly, where the lock is disengaged, the handle will be free to rotate relative to the plug element. Where the plug element for example is threaded into the filler tube, without an operative or drive connection between the handle and the plug element, the plug element cannot be removed from the filler tube. This therefore prevents unwanted third party access to the filler tube and attendant gas tank.
Under vehicular codes, there is a requirement that the gasoline storage tanks of automobiles and the like be made vapour tight to prevent the escape of gas vapours into the atmosphere. Typically, the requirement is that the gas tank be capable of withstanding pressure build up of at least one half an atmosphere above ambient pressure conditions. Such a pressure build up can be hazardous. More particularly, upon removal of a plug element from a pressurized gas tank, there is a risk of a rush of gas vapour and liquid, which can spill onto the person removing the gas cap. Gasoline may then come into contact with clothing and skin, which is less than ideal. Gasoline, being highly flammable, should not be allowed to soak a person's clothes. Also, staining is a problem.
To overcome this problem, some manufacturers have developed pressure release mechanisms associated with their locking gas caps. For example, U.S. Pat. No. 5,520,300 shows a lockable pressure relief fuel cap in which the pressure relief mechanism is associated with the locking mechanism. However, the means for actuating the vent, to release the overpressure in the fuel tank, operates only in response to movement of the lock from the locked position to the unlocked position. In other words, during the act of unlocking, the internal mechanism of this prior gas cap, causes a vent to open, to create a pressure release. This invention therefore includes a complicated series of posts, ramps and biasing elements to effect the translation of rotational movement into vent release movement. This is somewhat complicated and expensive to implement because of the number of parts required.
Other solutions, include a lockable pressure release mechanism for a radiator cap for a vehicle engine such as shown in U.S. Pat. No. 3,945,454. Radiator caps are substantially different from gas caps, and therefore are constructed according to different standards. Most particularly, radiator caps must stand significantly greater pressure build ups than one half of one atmosphere above ambient, which is the design level for gas caps.
U.S. Pat. No. 3,945,454, shows a radiator cap having a locking element which is a combination locking and unlocking device and pressure release device. However, according to this prior patent it is necessary, once the key is inserted to depress the key cylinder in the radiator cap sufficiently to permit a locking pin 41 to move a slider into locking engagement. The locking engagement connects the plug element to the handle element. Turning the key in the lock cylinder, without axial movement of the lock cylinder results in the locking pin idly turning and no locking engagement being made. This patent teaches that the lock cylinder must be moved axially a predetermined amount in order to lock the plug element to the handle. A pressure relief valve is located so that the valve is open when the locking element is moved axially enough to lock the plug element and the handle together.
Of course, in a radiator cap environment, where significant pressures are built up behind the cap, requiring a predetermined amount of axial movement of the lock cylinder, in order to open the valve a predetermined amount, is required. In the absence of such a requirement, a user would likely not provide sufficient force to act against the pressure built up within the radiator, to cause a pressure relief prior to removing the cap. Failing to adequately relieve the pressure prior to removing the radiator cap, could result in hot radiator fluid spewing out over the person removing the cap which is both unsafe and undesirable. However, requiring the movement of the locking element to be connected to the movement of the valve for the pressure release, requires extra components, and is complicated and expensive to implement.
Lefevre U.S. Pat. No. 5,667,093 Issue Date September 16, 1997 Wheat et al. U.S. Pat. No. 5,000,339 Issue Date March 19, 1991 Fukuta U.S. Pat. No. 4,579,244 Issue Date April 1, 1996